The preparation of pigmentary titanium dioxide by oxidizing titanium tetrachloride in the vapor state with an oxygen-containing gas is well known. Useful procedures therefore include those described in U.S. Pat. Nos. 2,488,439; 2,488,440; 2,559,638; and 2,833,627.
U.S. Pat. Nos. 2,488,439 and 2,488,440 also disclose that the addition of small, controlled amounts of water or hydrogenous water formers to the TiCl.sub.4 or oxidizing gas reactants promotes nucleation and production of a high quality pigment having a high carbon black undertone or CBU. CBU is described in U.S. Pat. No. 2,488,440 (which is hereby incorporated by reference) and is a measure of particle size. The higher the carbon black undertone, the smaller the particle size and the higher the quality of the pigment for many applications. However, at increased oxygen concentrations and a corresponding allowable increase in reactor throughput, water becomes a less effective nucleant.
U.S. Pat. No. 3,208,866 discloses generally an improvement in the production of TiO.sub.2 pigment by the oxidation of TiCl.sub.4 which comprises utilizing a metal ion nucleant selected from the group consisting of sodium, potassium, lithium, rubidium, cesium, calcium, barium, strontium and cerium. In accordance with such patent, incorporating the nucleant results in improved bulk density and carbon black undertone. Such patent also discloses that potassium chloride is preferred and that cesium chloride is less active than potasium chloride.
U.S. Pat. No. 3,505,091 describes another improvement in the production of TiO.sub.2 pigment by the oxidation of TiCl.sub.4 which comprises conducting the reaction at a pressure of about 20-400 pounds per square inch gage, in the presence of AlCl.sub.3. In accordance with such patent, the resulting TiO.sub.2 exhibits improved resistance to chalking.
U.S. Pat. No. 3,640,745 discloses a process for producing agglomerated pigmentary TiO.sub.2 by vapor phase oxidation of titanium halide in a reaction chamber at elevated temperatures in the presence of minor amounts of (1) an alkali metal, water soluble inorganic compounds of alkali metals or water insoluble organic compounds of alkali metals, (2) an auxiliary gas, and (3) minor amounts of water.
In modern processes for the production of TiO.sub.2 by the oxidation of TiCl.sub.4, potassium chloride is generally the preferred nucleant. Also in such modern processes, TiO.sub.2 often is produced in reactors (1) operating at high pressures to reduce process equipment size and lower investment, and/or (2) having a short residence time of the reactants in the mixing zone of the reactor to increase product output. At such high pressures and/or short residence times, however, it appears that the effectiveness of potassium chloride (especially with respect to carbon black undertone, gloss and specific surface areas) can be reduced. In addition, this reduction in effectiveness generally is apparent even if the concentration of potassium chloride is increased. Consequently, despite the above advances in TiO.sub.2 production technology, there exists a need for a nucleant which produces increased TiO.sub.2 carbon black undertone, specific surface area and gloss properties while operating at high pressures, short residence times of the reactants in the mixing zone of the reactor or both conditions. It should be noted that there is an increasing need for such TiO.sub.2 pigment because modern end uses increasingly require these properties.